Generally, there are two types of well-known electromagnetic clutches which include a structure to receive rotational and attractive forces; one type includes a plurality of leaf springs to receive the above forces and the other type includes a plurality of rubber members to receive these forces.
In the electromagnetic clutches including the leaf springs, when the electromagnetic clutch is energized, an armature plate is attracted to one end surface of a rotor against the recoil strength of the leaf springs. As the axial air gap between the armature plate and the rotor is made smaller, the higher attractive force is generated for attracting the armature plate to the rotor becomes higher. Therefore, the attractive velocity of the armature plate to the rotor also increases as the distance between the armature plate and the rotor is reduced. Although the attractive velocity of the armature plate to the rotor is low at the early stage of attracting motion, as the axial air gap becomes smaller, the attractive force becomes higher. The attractive force of the armature plate to the rotor is thus increasing when the velocity of the armature plate is likewise increasing. Therefore, when the armature plate is attracted to the rotor, large impact noise and vibration is produced between the armature plate and the rotor.
On the other hand, in an electromagnetic clutch which uses rubber members, durability of the rubber members and keeping the rubber members attached becomes a problem because when the armature plate is attracted to the rotor, great impact force in the rotational direction is applied to the rubber members.